1. Field of the Invention
The present invention relates generally to photopolymerizable materials, and more specifically to polymer-dispersed liquid crystal materials in which the switchable hologram performance parameters are subject to control and optimization.
2. Description of the Related Art
Demand for information has become a strong driver in many business, consumer, and government applications. Three key components of this demand are the storage, transmission, and display of information. The latter two in particular are placing severe demands on available hardware and software. In communications, there has been an explosion of traffic driven by the Internet, business data, and digital image transfers. In the end-point use of this huge data stream, visual utilization and management of data have high priority. Large data content requires high resolution (super video graphics array (“SVGA”) to extended graphics array (“XGA”)) along with full-color capability. The technological response to these challenges has spawned several innovations. For telecom applications, part of the response is to provide higher data rates and bandwidth extension through the use of dense wavelength division multiplexing (DWDM). For easy visual access to information, portable and handheld devices are evolving along with flat screens and personal displays. In addition, efforts are underway to make the advantages of digital video disc (“DVD”) and high definition television (“HDTV”) available in these formats.
Optics is at the core of all of these technologies. The information revolution is placing stringent demands on several optical components. For example, short- and long-period fiber Bragg gratings are playing key roles in the telecom industry, but the demand for multiple wavelengths and the ability for dynamic reconfiguration by DWDM is growing. In information display applications, the use of portable and micro-displays, combined with virtual display technology, is creating the need for complex off-axis optical systems in very compact, lightweight packages. This becomes impossibly heavy and cumbersome with conventional refractive and reflective optics.
Diffractive optics is the natural response to many of these demands. But these devices are by their very nature monochromatic. Multi-wavelength and dynamic reconfiguration capabilities are forcing a reconsideration of the use and fabrication of diffractive optical elements to satisfy the growing needs of the information revolution.
This revolution is creating demands for efficiency across a wide-range of applications. An approach developed to achieve such efficiency is through application specific performance, focusing on the parameters important for individual applications. Among these applications are: fiber optic switches; reprogrammable N×N optical interconnects for optical computing; beam steering for laser surgery; beam steering for laser radar; holographic image storage and retrieval; digital zoom optics (switchable holographic lenses); graphic arts and entertainment; and the like.
Switchable holographic optical elements (HOEs) have been invented to fulfill the promise of diffractive optics in meeting the technological challenges in telecom and information display. Multi-layered switchable holographic optical elements in a single solid-state device form a substitute for multiple static elements and complex refractive/reflective optical systems.
A hologram is an interference pattern that is recorded on a high-resolution recording plate. Two beams formed by a coherent beam from a laser interfere within the recording plate, causing an interference pattern. This pattern represents object information. The object information is a function of the light diffracted from the object to be recorded when the object is placed in the path of one of the two formation beams. If the resulting recording plate is viewed correctly in monochromatic light, a three-dimensional image of the object—a hologram—is seen. When forming a holographic grating, there is no object, per se, which is put into the path of one of the beams. Instead, given the wave properties of light, when two beams interact, they will form a grating within the recording plate. This grating can be formed so as to have any of a variety of characteristics.